A spray-dried dual microbial Wettable powder formulation: optimization and greenhouse efficacy against Western flower Thrips.

BACKGROUND: This study aimed to develop and evaluate a spray-dried wettable powder (WP) formulation containing the entomopathogenic bacterium Serratia marcescens and the fungus Metarhizium flavoviride for the control of Frankliniella occidentalis. RESULTS: The formulation was optimized using a Taguchi experimental design to maximize viable microorganism counts while maintaining suitable physicochemical properties. The optimal formulation achieved a high microbial load (3.18E+12 CFU/g) with favorable characteristics, including good suspensibility (79.4%), a low wetting time (27.4 s), an appropriate particle size (11.54 μm), and an acceptable moisture content (7.43%). The formulation also demonstrated strong thermal stability under different storage conditions. Laboratory bioassays revealed a clear dose-dependent increase in mortality in both larval and adult stages, with significant differences among treatment concentrations. The highest dose (100 g/100 L) consistently produced the greatest mortality. Greenhouse trials conducted in two different locations confirmed the efficacy of the formulation under practical conditions, achieving up to 92.6% control and showing performance comparable to that of a commercial product. CONCLUSION: These findings indicate that the combined use of bacterial and fungal agents in an optimized WP formulation provides an effective and sustainable alternative for the management of F. occidentalis. © 2026 Society of Chemical Industry.